The present disclosure relates to a sliding cam system for a variable valve train, to a variable valve train, to a motor vehicle and to a method for operating an internal combustion engine.
Valve-controlled internal combustion engines comprise one or more controllable inlet and outlet valves per cylinder. Variable valve control systems make flexible actuation of the valves possible in order to change the opening time, closing time and/or the valve lift. As a result, the engine operation can be adapted, for example, to a specific load situation.
DE 196 11 641 C1 has disclosed a valve train, by way of which the actuation of a gas exchange valve using a plurality of different lift curves is made possible. To this end, a sliding cam with at least one cam section which comprises a plurality of cam tracks is mounted on the camshaft fixedly so as to rotate with it but such that it can be displaced axially, which sliding cam comprises a lift contour, into which an actuator in the form of a pin is introduced radially from the outside in order to produce an axial displacement of the sliding cam. By way of the axial displacement of the sliding cam, a different valve lift is set at the respective gas exchange valve. After the axial displacement of the sliding cam relative to the camshaft, said sliding cam is latched in its axial relative position on the camshaft by virtue of the fact that at least one spring-loaded latching ball which is received and mounted in the camshaft engages into at least one latching groove in a manner which is dependent on the axial relative position. The axial displacement of the sliding cam in order to change the valve lift takes place exclusively in what is known as the base circle of the or each cam section or the cam tracks thereof. As a result, the switching rotational speed of the valve train is limited.
The shorter the base circles of the cams which coincide with one another, the less time is available for the axial displacement of the sliding cam. The less time is available for the axial displacement of the sliding cam system, the steeper the ramp of the switching guide plate (engagement track) has to be configured. In the case of the axial displacement of the sliding cam, considerable forces can occur in part in the case of the contact between the pin of the actuator and the switching guide plate. Particularly great forces can occur, in particular, in the case of steep ramps, which particularly great forces can have a negative influence on the service life of the sliding cam system and/or limit a maximum switching rotational speed.
DE 10 2012 112 482 A1 has disclosed a method for operating an internal combustion engine having a plurality of cylinders. In order to actuate gas exchange valves, the internal combustion engine comprises a valve train with at least one rotatably mounted camshaft and with at least one sliding cam which can be displaced axially on the respective camshaft. The respective sliding cam comprises at least one guide plate section with at least one groove which is configured on an outer circumferential face of the respective guide plate section, the respective sliding cam comprising at least one cam section with a plurality of cam tracks for setting different valve lifts. In order to bring about an axial displacement of the respective sliding cam, an actuable pin of an actuator is introduced radially from the outside into a groove of the guide plate section. The axial displacement of the respective sliding cam is carried out in a manner which is dependent on the axial displacement direction of said sliding cam and/or in a manner which is dependent on a valve play outside a base circle of the or each cam section of said sliding cam.